High-integration and high-performance of a semiconductor integrated circuit have been achieved by miniaturizing the semiconductor integrated circuit. However, now that pattern sizes are reduced to nanometer dimensions, miniaturization of the semiconductor integrated circuit no more guarantees performance improvement.
Thus, as one technique to accomplish the performance improvement of the integrated circuit, attention is being paid to a technique of using an insulating film having a lower dielectric constant than that of an inorganic silicon oxide film (hereinafter, simply referred to as a Low-k film or a low dielectric insulating film) as an interlayer insulating film. A decrease of the dielectric constant of the interlayer insulating film results in a reduction of parasitic capacitance of wiring in the integrated circuit, and the reduction of the parasitic capacitance of the wiring in turn causes an increase of a signal transmission speed, thus enabling the performance improvement of the integrated circuit.
However, the Low-k film as the interlayer insulating film has a lower strength than the general inorganic silicon oxide film. Therefore, the Low-k film suffers damage while etching for pattern formation or ashing of photoresist is performed. As a result, the dielectric constant of the Low-k film increases.
To recover such damages, Patent Reference 1 (Japanese Patent Laid-open Application No. 2006-49798) discloses a method of reforming a damaged portion with a silylizing agent after the etching or ashing, that is, after the pattern formation.
However, inventors of the present application have conducted many researches and found out that a Low-k film having a damaged layer tends to adsorb moisture (H2O) easily. It is deemed to be because the surface of the Low-k film having the damaged layer becomes hydrophilic. The moisture adsorbed by the Low-k film causes oxidation of a metal, e.g., wiring, buried in the Low-k film.
Furthermore, since the surface of the Low-k film is in the hydrophilic state, a cleaning solution may not be sufficiently removed in a wet cleaning process performed after a heat treatment, and it may become one factor that causes a generation of pattern defaults.
If the heat treatment is performed on the Low-k film after the pattern formation, the adsorbed moisture is evaporated from the Low-k film, whereby the oxidation of the buried metal or the generation of the pattern defaults can be prevented effectively.
However, the heat treatment alone cannot restore damaged components in the damaged layer of the Low-k film sufficiently. Therefore, the dielectric constant of the Low-k film would still remain shifted to a high level, so that electrical characteristics of the Low-k film cannot be recovered sufficiently.